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Intracellular Ca 2+ Homeostasis in Trypomastigotes of Trypanosoma cruzi
Author(s) -
Zhang Hong Shan,
McDonald Thomas V.,
Tanowitz Herbert B.,
Wittner Murray,
Weiss Louis M.,
Bilezikian John P.,
Morris Stephen A.
Publication year - 1998
Publication title -
journal of eukaryotic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 1066-5234
DOI - 10.1111/j.1550-7408.1998.tb05073.x
Subject(s) - ionomycin , thapsigargin , extracellular , intracellular , monensin , biology , nigericin , homeostasis , biophysics , phospholipase c , microbiology and biotechnology , biochemistry , signal transduction , membrane
Trypomastigotes of Trypanosoma cruzi maintain an intracellular Ca 2+ concentration([Ca 2+ ] i ) of 64 ± 30 nM. Equilibration of trypomastigotes in an extracellular buffer containing 0.5 mM [Ca 2+ ] o (preloaded cells) increased [Ca 2+ ] i < 20 nM whereas total cell Ca 2+ increased by 1.5 to 2.0 pmole/cell. This amount of Ca 2+ would be expected to increase [Ca 2+ ] i to > 10 μM suggesting active sequestration of Ca 2+ . We tested the hypothesis that maintenance of [Ca 2+ ] i involved both the sequestration into intracellular storage sites and extrusion into the extracellular space. Pharmacological probes known to influence [Ca 2+ ] i through well characterized pathways in higher eukaryotic cells were employed. [Ca 2+ ], responses in the presence or absence of [Ca 2+ ]o were measured to asses the relative contribution of sequestration or extrusion processes in [Ca 2+ ] i homeostasis. In the presence of 0.5 mM [Ca 2+ ] o , the ability of several agents to increase [Ca 2+ ] i was magnified in the order ionomycin ⋙ nigericin > thapsigargin > monensin > valinomycin. In contrast, preloading markedly enhanced the increase in [Ca 2+ ], observed only in response to monensin. Manoalide, an inhibitor of phospholipase A 2 , enhanced the accumulation of [Ca 2+ ] i due to all agents tested, particularly ionomycin and thapsigargin. Our results suggest that sequestration of [Ca 2+ ] i involved storage sites sensitive to monensin and ionomycin whereas extrusion of Ca 2+ may involve phospholipase A 2 activity. A Na + /Ca 2+ exchange mechanism did not appear to contribute to Ca 2+ homeostasis.